Abstract: Regeneration of oak species is essential for maintaining the structure of woodland ecosystems across the Inner Coast Range, but recruitment of certain species has slowed in recent years. Our study examines the balance between seed predation, which limits oak regeneration, and seedling growth enhancement caused by rising CO2 levels. If seedlings can survive their most vulnerable life stages, California’s native oaks may yet survive in the region. California’s native blue oak (Quercus douglasii) is of particular interest due to its demonstrated xeric tolerance, but the average age of blue oaks is very high, signaling a lack of seedling establishment in recent decades. This pattern is not well understood, and our study seeks to determine whether rising CO2 levels and preferential seed predation play a role. Using screen-aided CO2 control over sixteen one-meter plots at Quail Ridge Reserve, oak seedlings have been subjected to two treatments: ambient CO2 and elevated CO2 (+105 ppm). Data recorded includes initial seed mass, germination success, height and basal diameter of seedlings, leaf count and leaf length, and qualitative measures of plant health. We have shown that elevated CO2 is significantly (p=0.0292) and positively linked to improved health of oak seedlings and positively linked to seedling height (p=0.0893). We control for otherwise hypothesized reasons for decreased seedling establishment – fire, large-animal herbivory, and competition with native grasses – through exclosures and weeding efforts. However, upon initial planting of blue oak acorns, we observed substantial small-animal herbivory of the acorns. After attempts to germinate blue oaks in the field failed due to herbivory, we decided to continue the CO2 experiments in a greenhouse. Field-based experiments with live and/or camera traps will provide insight into the importance of seed predation as a filter on blue oak regeneration. Investigating the relative importance of seed predation and CO2 effects on blue oak regeneration will give us an understanding of the species’ future in the Inner Coast Range. If blue oak establishment remains at its current critically low levels, woodland composition and habitat structure in California’s Inner Coast Range will change significantly. Species that rely on blue oaks, directly or indirectly, may experience dramatic shifts in their survival outlooks, ultimately altering biodiversity across the region. Determining the effect of elevated CO2 and seed predation on blue oak seedling growth and survival will provide insight into the future of this species and those that rely on it.
